package test_3_7;

import java.util.Scanner;

public class six {
    public static void main(String[] args) {
        Scanner sc=new Scanner(System.in);
        int n=sc.nextInt();
        int sum=0;
        for(int i=1;i<=n;i++)
        {
            sum+=N(i);
        }
        System.out.println(sum);
    }
    public static int N(int n)
    {
        if(n<=1)
        {
            return n;
        }
        else {
            return n*N(n-1);
        }
    }
}
